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Darwin Correspondence Project

From G. H. K. Thwaites   8 June 1863

Peradenia, Ceylon

8 June 1863

My dear Darwin,

It gave me great delight to find from your last welcome letter that the specimens I sent you proved so interesting.1 Be assured you shall be made acquainted with every fact that comes before me which seems to me to bear upon your most valuable & interesting researches. With this you will receive some seeds of the Limnanthemum Indicum, which you will probably be able to cultivate in a pan of water in your hothouse.2

Very many thanks for your little brochure on dimorphism in Linum.3 It seems to me that there is a great analogy between the behaviours of the pollen grains in phænogams and what we observe in the cells of some of the lower Algæ (Zygnema for instance): for in one species of the last named genus we find a regular conjugation taking place between the cells of separate filaments


whilst in another species we have the adjoining cells of the same filament conjugating inter se, thus


—and, if my memory does not deceive me, there are cases where there is apparently no conjugation,


and I should be inclined to consider, under this view, that the differentiation you refer to in the second paragraph of p. 75 respecting Linum grandiflorum, is one of polarity rather than of a tendency to specific distinction;4 but then again the question arises whether the process of specific differentiation is not coincident with modification of polarity or, what may be considered much the same thing, chemical affinity.

I enclose a letter I have just received from my very intelligent and accomplished correspondent, the Revd S. O. Glenie, Chaplain at Trincomalie, who with his good lady are quite enthusiastic in the study of botany, and with his letter is also the specimen of the flower of Cassia Fistula he refers to.5

I have requested him to keep his attention alive to cases of dimorphism in all the plants he examines. He takes great interest in your researches, but I don’t at all know how far he goes with you.

Believe me always | truly & sincerely your’s | G. H. K. Thwaites

P.S. Our dear friend Sir William Hooker has just sent me his Carte de Visite,6 a most acceptable present, as you may believe; I need scarcely tell you how much I should be gratified with one of you, if you have had it taken.


Trincomale 5: June 1863 My dear Sir

I send in the accompanying packet a specimen of a lovely Nauclea I gathered this morning in some neglected ground near the Cuteherry where the tree (a small one) had doubtless been planted in better days. Is this the Nauclea coadunata Roxb; 7 DeC: 4.344 & Enum: 137.—8 As far as I can gather from a careful examination the description of C. coadunata, (not a very full one by the bye) applies pretty well to my specimen but I do not feel at all certain—

The Cassia Fistula L 9 formed the subject of our study this morning, & a careful exhaustive study we made of it.

I enclose the stamens for your inspection premising that in 12 flowers at least I have found exactly the same appearance.

W. & A.: page 285 say the anthers have two clefts10   Now I make out that the three (longer) lower, and the right and left of the the three (shorter) upper anthers have two clefts, while the middle one of the three lower and the four central anthers open by powers. This is a curious mingling of the two modes of discharging pollen, and worthy, I think, of notice.

I hope you will not look upon it as a trifle beneath notice, for I learn everyday the necessity of not passing over trifles—

Believe me | As Ever Yours sincerely | S. O. Glenie

Did you observe the sweet honey-like substance on the calyx of the Diospyros I forwarded a few days ago?—

CD annotations

1.1 I send … better days. 1.3] ‘Gradation’ brown crayon, circled brown crayon
4.3 the middle … notice. 4.5] scored brown crayon
Top of enclosure: ‘[Inter]ink, del ink; ‘Gradation’ ink, circled ink


Thwaites’s name appears on CD’s presentation list for ‘Two forms in species of Linum (see Correspondence vol. 11, Appendix IV).
In ‘Two forms in species of Linum, p. 75 (Collected papers 2: 98), CD stated: Taking fertility as the criterion of distinctness, it is no exaggeration to say that the pollen of the long-styled Linum grandiflorum (and conversely of the other form) has been differentiated, with respect to the stigmas of all the flowers of the same form, to a degree corresponding with that of distinct species of the same genus, or even of species of distinct genera.
The references are to Samuel Owen Glenie, and possibly to his second wife Mary Elizabeth Louisa Glenie.
William Jackson Hooker.
William Roxburgh (Taxonomic literature).
Candolle and Candolle 1824–73, 4: 344, and Thwaites 1858–64, p. 137.
The ‘L’ denotes Carolus Linnaeus (Taxonomic literature).
Wight and Arnott 1834.


Candolle, Augustin Pyramus de and Candolle, Alphonse de. 1824–73. Prodromus systematis naturalis regni vegetabilis, sive enumeratio contracta ordinum generum specierumque plantarum huc usque cognitarum, juxta methodi naturalis normas digesta. 19 vols. Paris: Treuttel & Würtz [and others].

Collected papers: The collected papers of Charles Darwin. Edited by Paul H. Barrett. 2 vols. Chicago and London: University of Chicago Press. 1977.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Taxonomic literature: Taxonomic literature. A selective guide to botanical publications and collections with dates, commentaries and types. By Frans A. Stafleu and Richard S. Cowan. 2d edition. 7 vols. Utrecht, Netherlands: Bohn, Scheltema & Holkema. The Hague, Netherlands: W. Junk. 1976–88.

Thwaites, George Henry Kendrick. 1858–64. Enumeratio plantarum Zeylaniæ: an enumeration of Ceylon plants, with descriptions of the new and little-known genera and species, observations on their habits, uses, native names, etc. Assisted in the identification of the species and synonymy by J. D. Hooker. 5 pts. London: William Pamplin; Dulau & Co.

‘Two forms in species of Linum’: On the existence of two forms, and on their reciprocal sexual relation, in several species of the genus Linum. By Charles Darwin. [Read 5 February 1863.] Journal of the Proceedings of the Linnean Society (Botany) 7 (1864): 69–83. [Collected papers 2: 93–105.]


Dimorphism in Linum.

Situation in some of the lower Algae is analogous to that in phaenogams. In some, conjugation occurs between separate filaments, in others between cells of same filament.

Forwards a letter from S. O. Glenie enclosing specimens of Cassia fistula which show the two forms of the anthers.

Letter details

Letter no.
George Henry Kendrick Thwaites
Charles Robert Darwin
Sent from
Peradeniya, Ceylon
Source of text
DAR 178: 121–2
Physical description
3pp enc, ALS 4pp †(by CD)

Please cite as

Darwin Correspondence Project, “Letter no. 4208,” accessed on 23 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 11